Devices for accomplishing the above-stated objective are known, and are typically mounted on a boom-like member of a back hoe or other large earth equipment used in the construction industry. Examples of prior art relating to this invention are U.S. Pat. No. 4,785,893 issued to Kistner on Nov. 22, 1988 and U.S. Pat. No. 4,867,253 issued to Eftefield et al on Sep. 19, 1989.
Because of the very severe environment in which such devices are used, primarily in the demolition or breaking of concrete roads at the outset of a reconstruction program where abrasive particles and dust are flying in all directions, and because of the tremendous forces used in the concrete destruction, the impacting devices are normally subject to rapid wear, frequent servicing and parts replacement. The bearing surfaces supporting power and actuator plungers of the impacters require lubrication, but the lubrication itself can become a carrier for the grit and dust from the concrete, not only into the bearings, but oftentimes directly into the shielded housing or casing which support the plunger actuating mechanisms and a compression spring for firing the power plunger. Once bearing wear starts, it often progresses rapidly. The plungers are then subject to becoming misaligned relative to each other, causing uneven wear of the internal trigger mechanism as a result. Loading of the compression spring preparatory to firing the power plunger inherently tends to impart torsion to the power plunger, possibly causing internal scoring and galling of its casing as well as of the trigger mechanism. The more complicated the trigger and latching members are and the greater the number of movable parts, the greater the frequency of parts replacement due to the destructive abrasiveness of the materials in the environment and the tremendous forces to which the operating parts are subjected. Of necessity, the more frequently parts must be replaced, the greater the need to utilize removable fasteners to facilitate parts replacement. Nut and bolt type fasteners are more likely to break down faster than a weld, for example, from the constant high pounding they take during breaking concrete. Additionally, prior art trigger and latching mechanisms were subjected to severe forces in order to effect release, since the compression spring is preloaded to near its maximum at the time the trigger must go over center against the spring force to release the latch. The added force required to release the trigger and latching mechanism resulted in an increase in the rate of wear of the loaded parts.